In a typical refinery set up, crude oils are subjected to atmospheric distillation to separate lighter materials such as gas oils, kerosenes, gasolines, straight run naphtha, etc. from the heavier materials. The residue from the atmospheric distillation step is then distilled at a pressure below atmospheric. This latter distillation step produces a vacuum gas oil distillate and a vacuum reduced residual oil which often contains asphalts, resins, and heavy hydrocarbonaceous oil components. Upgrading vacuum resid is important in that these oils are often used as feedstocks for lubricating oil manufacture.
There are a number of techniques used for recovering the useful oils from various asphaltic petroleum residual oils. Many such processes involve the extraction of the oil with a deasphalting solvent such as propane, and thereafter separating and recovering the oil components from the solvent. In U.S. Pat. No. 2,950,244, a process for the extraction of petroleum residue containing asphalt is disclosed. The solvent utilized is a liquefied normally gaseous solvent, such as propane, which is maintained at a temperature between 100.degree. and 200.degree. F. and at a pressure sufficient to maintain the solvent in a liquid phase.
Variations of the deasphalting process using propane or similar short chain aliphatics as solvents are shown in U.S. Pat. No. 2,669,538 to Yurasko et al; U.S. Pat. No. 3,516,928 to King et al, issued June 23, 1970; U.S. Pat. No. 4,017,383 to Beavon, issued Apr. 12, 1977; and U.S. Pat. No. 4,201,660 to Szosel, issued May 6, 1980. King et al additionally suggests that carbon dioxide and ammonia, are under certain circumstance, equivalent as solvents to the disclosed lower alkanes, alkenes and their halogenated derivatives.
While propane is often used in known deasphalting operations, other solvents have been suggested. In U.S. Pat. No. 4,054,512, an asphalt-containing mineral oil is deasphalted by contacting the oil with liquid hydrogen sulfide. The use of liquid neopentane, at a temperature between 0.degree. and 250.degree. F., as the deasphalting solvent is shown in U.S. Pat. No. 3,334,043. In U.S. Pat. No. 2,337,448, heavy residual oil is deasphalted by a solvent selected from the group made up of ethane, ethylene, propane, propylene, butane, butylene, isobutane, and mixtures thereof.
Multi-stage solvent extraction techniques involving the use of one or more solvents are also known. In U.S. Pat. No. 3,658,665 a heavy oil is subjected to a two-stage extraction process. In the first stage, the heavy oil is contacted with a solvent and the mixture is thereupon subjected to additional solvent in a second zone. The second zone is maintained at a higher temperature than is the first solvent stage. In U.S. Pat. No. 4,017,383, a multistage deasphalting process is shown in which the recovery of the solvent from the extracted hydrocarbon is effected in a series of two or more pressure stages. The solvents are liquefied low molecular weight hydrocarbons, such as propane or isobutane.
Additionally there are a number of processes which use multiple or mixed solvents to deasphalt various oils. For instance, in U.S. Pat. No. 2,188,051 to Lantz, issued Jan. 23, 1940, the oil is contacted with a solvent preferably containing at least 75% of paraffinic hydrocarbons having less than seven carbon atoms. Ethane, propane, butane, isobutane, the pentanes, the heptanes, and the hexanes constitute the preferred solvents. The hydrocarbon solvent is first mixed with carbon dioxide for subsequent addition to the oils to be extracted.
In U.S. Pat. No. 2,631,966 to Francis, issued Mar. 17, 1953, liquid carbon dioxide and a variety of other solvents are used to separate various portions of the hydrocarbon feed. The solvents are members of two distinct classes. The first class is one whose members are completely miscible with liquid carbon dioxide but incompletely miscible with the oil to be extracted. The second class involves solvents which are incompletely miscible with carbon dioxide and also incompletely miscible with the feedstock to be extracted. Both sets of solvents are further defined to be those which do not form a solid salt with carbon dioxide at temperatures of 20.degree. C. or higher. Included in the first class of solvents are such compounds as dichlorodiethyl ether, isopropanol, beta-ethoxy ethanol, diethylene glycol monoethyl ether and the like. Members of the second class of solvents include aniline, o-chloroaniline, m-chloroaniline, cresols and the like. The process generally includes the steps of adding the mixture of carbon dioxide and solvent to the oil and removing the carbon dioxide at various stages to effect separation of various types of hydrocarbon oils. U.S. Pat. No. 2,646,387 also to Francis, issued July 21, 1953, suggests an improvement to the process discussed above. The improvement identifies a method of recovering the solvent from the hydrocarbon oil by addition of liquid carbon dioxide to the solvent-oil mixture so as to form a solvent-carbon dioxide phase.
U.S. Pat. No. 4,179,362 to Irani et al, issued Dec. 18, 1979, suggests the separation of petroleum fractions into aromatic-rich and paraffinic-rich hydrocarbon streams by the use of methanol/water mixtures. The paraffin-rich stream is recovered as raffinate and aromatic-rich stream as the extract. After the extraction step, additional water is added to the extract and raffinate streams where the water acts as an antisolvent to effect separation of the hydrocarbon from the solvent. The water and methanol are then separated either by flash distillation or by using supercritical carbon dioxide as an extraction solvent.
In U.S. Pat. No. 4,191,639 to Audeh et al, issued Mar. 4, 1980, hydrocarbon oils such as residual petroleum oils are deasphalted and demetallized by contact with a liquid mixture of at least two of the components selected from hydrogen sulfide, carbon dioxide, and propane.
None of the above references are believed to suggest a process in which a heavy oil is deasphalted, the solvent extract is expanded or diluted using an expansion gas, such as carbon dioxide, to produce liquid product aromatics, and the remaining liquid phase is flashed to reconstitute the expansion gas, a solvent-containing stream, and a product saturate stream.